Carotenoids are a class of naturally occurring pigments found in trace amounts in the tissues of higher plants, algae, bacteria and fungi. Carotenoids are polyenes having a C.sub.40 carbon skeleton (phytoene) which contains an extended network of single and double bonds. The various carotenoids are formed by chemically modifying this C.sub.40 carbon skeleton. For example, dehydrogenation of phytoene yields the carotenoid lycopene which is responsible for the color of tomatoes and cyclization of both ends of lycopene yields the carotenoid .beta.-carotene which is responsible for the color of carrots.
Carotenoids, such as .beta.-carotene, are valuable pigments useful for coloring various comestibles, such as margarine, as they avoid the health concerns associated with synthetic pigments and actually possess significant nutritional value (.beta.-carotene is a precursor to the formation of retinal and vitamin A in humans).
Because carotenoids occur naturally in only trace amounts, the carotenoids must be extracted in concentrated form in order to be useful. Ordinarily, carotenoids are extracted from natural sources by treating the material with a carotenoid-solubilizing hydrocarbon solvent, such as hexane, or chloroform, separating the carotenoid-containing hydrocarbon solvent from the remainder of the material, and then driving off the hydrocarbon solvent to produce a carotenoid-enriched solid product.
In addition to carotenoids, plants contain a variety of other constituents which are soluble in hydrocarbon solvents such as various proteins and lipids. Accordingly, the carotenoid-enriched solid product typically includes significant amounts of other components in addition to the carotenoid(s).
Use of a hydrocarbon solvent to extract the carotenoids significantly increases the cost and complexity of the extraction procedure due to the cost of the hydrocarbon solvent, the cost of removing the hydrocarbon solvent from the final product, the cost of recovering the removed hydrocarbon solvent, and the cost of disposing of contaminated hydrocarbon solvent which cannot be reused. In addition, use of a hydrocarbon solvent to effect extraction of carotenoids results in significant environmental damage due to the release of hydrocarbon fumes into the atmosphere and the need to dispose of contaminated hydrocarbon solvent which cannot be reused.
Accordingly, a substantial need exists for a simple and environmentally safe process of extracting carotenoids from carotenoid-containing natural sources which avoids the need to utilize a hydrocarbon solvent.